tailieunhanh - Lecture Organic chemistry: Chapter 2 - L. G. Wade, Jr.
Chapter 2 - Structure and properties of organic molecules. To understand these aspects of molecular structure we need to consider how the atomic orbitals on an atom mix to form hybrid atomic orbitals and how orbitals on different atoms combine to form molecular orbitals. In this chapter, we look more closely at how combinations of orbitals account for the shapes and properties we observe in organic molecules. | Chapter 2 © 2010, Prentice Hall Organic Chemistry, 7th Edition L. G. Wade, Jr. Structure and Properties of Organic Molecules Chapter 2 Wave Properties of Electrons Standing wave vibrates in fixed location. Wave function, , is a mathematical description of size, shape, and orientation. Amplitude may be positive or negative. Node: Amplitude is zero. Chapter 2 Wave Interactions Linear combination of atomic orbitals: between different atoms is bond formation. on the same atom is hybridization. Conservation of orbitals Waves that are in phase add together. Amplitude increases. Waves that are out of phase cancel out. Chapter 2 Sigma Bonding Electron density lies between the nuclei. A bond may be formed by s—s, p—p, s—p, or hybridized orbital overlaps. The bonding molecular orbital (MO) is lower in energy than the original atomic orbitals. The antibonding MO is higher in energy than the atomic orbitals. Chapter 2 s Bonding MO Formation of a s-bonding MO: . | Chapter 2 © 2010, Prentice Hall Organic Chemistry, 7th Edition L. G. Wade, Jr. Structure and Properties of Organic Molecules Chapter 2 Wave Properties of Electrons Standing wave vibrates in fixed location. Wave function, , is a mathematical description of size, shape, and orientation. Amplitude may be positive or negative. Node: Amplitude is zero. Chapter 2 Wave Interactions Linear combination of atomic orbitals: between different atoms is bond formation. on the same atom is hybridization. Conservation of orbitals Waves that are in phase add together. Amplitude increases. Waves that are out of phase cancel out. Chapter 2 Sigma Bonding Electron density lies between the nuclei. A bond may be formed by s—s, p—p, s—p, or hybridized orbital overlaps. The bonding molecular orbital (MO) is lower in energy than the original atomic orbitals. The antibonding MO is higher in energy than the atomic orbitals. Chapter 2 s Bonding MO Formation of a s-bonding MO: When the 1s orbitals of two hydrogen atoms overlap in phase with each other, they interact constructively to form a bonding MO. Chapter 2 s* Antibonding MO Formation of a s* antibonding MO: When two 1s orbitals overlap out of phase, they interact destructively to form an antibonding MO. Chapter 2 H2: s—s Overlap Chapter 2 Cl2: p—p Overlap When two p orbitals overlap along the line between the nuclei, a bonding orbital and an antibonding orbital result. Most of the electron density is centered along the line between the nuclei. This linear overlap is another type of sigma bonding MO. Solved Problem 1 Chapter 2 Draw the s* antibonding orbital that results from the destructive overlap of the two px orbitals just shown. This orbital results from the destructive overlap of lobes of the two p orbitals with opposite phases. If the signs are reversed on one of the orbitals, adding the two orbitals gives an antibonding orbital with a node separating the two nuclei:
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